Wood-burning boilers are known in the industry. Typically wood-burning boilers are disposed exterior to and away from the structure to be heated. Water lines extend from the wood-burning boiler to the structure to be heated, where the heated water is circulated and the cooled return water is returned to the wood-burning boiler.
Combustion in the wood-burning boiler is typically enhanced by forcing air into the boiler in order to make the combustion process more efficient. Additionally, by denying the forced air, the boiler can be cooled between periods of heating. In this manner, the wood-burning boiler may be thermostatically controlled by a thermostat located in the structure to be heated that controls the fan for forcing air into the wood-burning boiler.
There is a need in the industry to increase the efficiency of wood-burning boilers. There are three stages of combustion of wood, which are described in Heating with Wood: Principals of Combustion, by Michael Vogel, Montana State University, reprinted March 2003, the disclosure of which is hereby incorporated by reference in its entirety. The first stage of wood combustion is the heating and evaporating stage, wherein water within the wood is boiled, and also, volatile gases begin to be generated. The second stage of wood combustion is the heat-producing stage, during which primary and secondary combustion takes place. Primary combustion is the process by which gases are released from wood and burned, and takes place in the range of 500 to 900 degrees Fahrenheit. Primary combustion produces large byproducts of unburned combustible gases, which contain a large amount of potential heat from the wood. In order for these gases to be burned, sufficient oxygen is needed as well as temperatures over 1100 degrees Fahrenheit, conditions which are not normally present in typical wood burning stoves. The air supply amount is critical, as too little air will not support combustion, yet too much air will cool the gaseous mixture, preventing combustion. The third stage of wood combustion is the charcoal stage, having a burn temperature exceeding 1100 degrees Fahrenheit.
Accordingly, there is a need in the industry for a wood-burning boiler that more efficiently combusts wood.